The setting was seemingly random: an outer gate at the Pentagon at evening rush hour. But John Patrick Bedell’s violent rampage Thursday made him only the latest in the growing ranks of the disaffected and disturbed to take aim at a symbol of official Washington.

The shooting contained jarring echoes of other recent attacks, from last month’s plane crash at an IRS building in Texas to the shooting last June of a museum guard at the U.S. Holocaust Memorial Museum in the District. Although the circumstances differ greatly, all were acts of rage by men who blamed their personal misfortunes on what they perceived to be sinister forces within the government.

All three also appear to have drawn ideological nourishment from the same well: online communities of like-minded people who validate and amplify extreme views. Today, more than in recent years, such communities are tapping into a broad undercurrent of anti-government discontent fueled by economic recession, joblessness and concern over the growing federal deficit, according to experts who have studied the phenomenon.

For Bedell and others like him, Washington and its institutions are an irresistible target — the “ultimate symbol of power for the powerless,” said Jerrold Post, a professor of political psychology at George Washington University.